How can I calculate a 28.5 mm hole for a hyperboloid center opening when it's Z=0
If you want to input the radius here:

You can change your code by:
for i in range (0, num_x):
    for j in range(0,num_y):
        # nomalize range
        
        u = 8*(i/num_x-1/2)
        v = 2*math.pi*(j/(num_y-1)-1/2)
        
        x = math.sqrt(1+u*u)*math.cos(v)*uval_a/2
        y = math.sqrt(1+u*u)*math.sin(v)*uval_a/2
        z = uval_b*u
        
        vert = (x,y,z)
        verts.append(vert)

As explained here
The base equation is:
$$
\frac{x^2}{a^2} - \frac{y^2}{b^2} = 1
$$
Which gives:
$$
y = \pm \frac{b}{a} \sqrt{x^2 - a^2}
$$
When a and b are defined by: